The present invention relates to improved modified asphalt characterized by better binding of the modifier material to the asphalt.
The addition of polymers to asphalt improves the physical and mechanical properties of the asphalt. The most commonly used polymers are styrene butadiene styrene (SBS), styrene butadiene (SB) and styrene butadiene rubber (SBR). Polymer modified asphalts (PMA) are used in pavement and roofing materials. Modified asphalts and asphalt emulsions are primarily produced through conjugated-diene backbone type polymers.
A number of techniques are currently used to link polymers with asphalt. One technique is to use asphalt binders. However, such binders do not meet all of the requirements developed by the SUPERPAVE protocol. Inferior binders result in damage to asphalt pavement including permanent deformation, thermal cracking and flex fatigue. These damages diminish the life of the pavement.
Another linking technique uses additives to assist with coupling the polymer modifier material to asphalt molecules to produce polymer modified asphalts. These coupling additives include alkyl polysulfide, poly phosphoric acid, dithio carbamates, phosphorous penta-sulfide, 4-4xe2x80x2-dithiomorpholine, furfural, thiozole derivatives, phosphorous penta oxide, hydrogen peroxide sodium hydroxide, and sulfur trioxide.
A major drawback of conventional polymer modified asphalts is that the asphalt develops a gel in certain portions thereof resulting from over-reactivity of the linking or activator material with the modifier material. This is particularly the case where polymer modified asphalt is stored prior to installation. Gel formation makes the polymer modified asphalt difficult to work with and install.
Polymer modified asphalts are well-known in the prior art as evidenced by the U.S. Pat. No. 6,444,731 to Memon, U.S. Pat. No. 6,451,886 to Krivohlavek and U.S. Pat. No. 6,429,241 to Liang and by published U.S. patent application No. 20020111401 to Izumoto. These references disclose the use of different linking additives to generate stable polymer modified asphalt, especially for polymers including conjugated-diene. The modified asphalts are stable in the storage and are easy to transport.
However, a major drawback of modified asphalts according to the prior art is the over-reactivility of the linking agent or activator with the polymer during storage. Thus, over time, a gelatinous mass is formed within the asphalt which inhibits the uniformity of the mixture and makes the modified asphalt difficult to handle and apply.
The present invention was developed in order to overcome these and other drawbacks of the prior modified asphalts by providing an anti-gelatinous carrier with the activator material to prevent gel formation and provide a smoother polymer modified asphalt.
Accordingly, the present invention relates to a method for making a modified asphalt in which a modifier material is mixed with hot asphalt to form an asphalt mixture and in which a carrier material is mixed with a hot activator material to form a carrier slurry. The carrier and activator materials have similar gravity properties to facilitate mixing thereof. The carrier slurry is then mixed with the asphalt mixture to produce a modified asphalt having improved rheological, separation and solubility characteristics.
The modifier material is preferably a polymer or granular crumb rubber. Suitable polymers include styrene butadiene styrene (SBS), styrene butadiene (SB) and styrene butadiene rubber (SBR). The activator is preferably an acid containing a trace amount of sulfur and the carrier is mineral oil.